1. Field of the Invention
The present invention relates to a process for preparing 4-aminodiphenylamine intermediates.
2. Related Art
4-Aminodiphenylamines are widely used as intermediates in the manufacture of alkylated derivatives having utility as antiozonants and antioxidants, as stabilizers for monomers and polymers, and in various specialty applications. For example, reductive alkylation of 4-aminodiphenylamine (4-ADPA) with methylisobutyl ketone provides N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylene-diamine, which is a useful antiozonant for the protection of various rubber products.
4-Aminodiphenylamine derivatives can be prepared in various ways. An attractive synthesis is the reaction of an optionally substituted aniline with an optionally substituted nitrobenzene in the presence of a base, as disclosed, for example, in U.S. Pat. No. 5,608,111 (to Stern et al.) and U.S. Pat. No. 5,739,403 (to Reinartz et al.). U.S. Pat. No. 5,608,111 describes a process for the preparation of an optionally substituted 4-ADPA wherein in a first step optionally substituted aniline and optionally substituted nitrobenzene are reacted (coupled) in the presence of a base. In working examples, aniline and nitrobenzene are reacted in the presence of tetramethylammonium hydroxide as the base, and water and aniline are azeotropically removed during the coupling reaction.
International publication WO 00/35853 discloses a method of preparation of intermediates of 4-aminodiphenylamine by the reaction of aniline with nitrobenzene in a liquid medium where the reaction system consists of a solution of salts of true zwitterions with hydroxides. A combination of potassium hydroxide and betaine hydrate is exemplified. The reaction may take place in the presence of free oxygen.
EP publication 566 783 describes a method of manufacture of 4-nitrodiphenylamine by the reaction of nitrobenzene with aniline in the medium of a polar aprotic solvent in a strongly alkaline reaction system. A phase transfer catalyst such as tetrabutylammonium hydrogen sulfate is employed. This reference requires that the reaction be carried out in an oxygen-free atmosphere in order to prevent undesirable side reactions caused by oxidation.
U.S. Pat. No. 5,117,063 and International publication WO 01/14312 disclose processes for preparing 4-nitrodiphenylamine and 4-nitrosodiphenhylamine, using various bases, including tetraalkylammonium hydroxides alone or an inorganic base with crown ether as a phase transfer catalyst. The use of aerobic conditions is described, including by example. Less azobenzene is reported for reactions at anaerobic conditions with aniline as the solvent or at aerobic conditions with DMSO, and other similar solvents, as the solvent.
U.S. Pat. No. 5,612,483 describes a process for preparing nitro substituted arylamines, including 4-nitro-diphenylamine, comprising reaction of an aryl amine with a nitroaryl amine, in the presence of bases while introducing oxygen in polar solvents. The patent states that the reactions lead to good yields of the corresponding amines with the use of simple bases, preferably inorganic bases.
U.S. Pat. No. 6,140,538 describes a process for preparing an optionally substituted 4-aminodiphenylamine comprising reacting an optionally substituted aniline and an optionally substituted nitrobenzene in the presence of water and a base while controlling the water content so as to ensure a molar ratio of water to the base charged of not less than about 4:1 at the start of the coupling reaction and not less than about 0.6:1 at the end of the coupling reaction to produce 4-nitrodiphenylamine and/or 4-nitrosodiphenylamine and/or salts thereof. The coupling reaction is followed by a hydrogenation reaction where the coupling reaction product is hydrogenated in the presence of a hydrogenation catalyst and added water so as to ensure a molar ratio of total water to base of at least about 4:1 at the end of hydrogenation. Aqueous and organic phases are obtained and the optionally substituted 4-aminodiphenylamine is recovered from the organic phase and the aqueous phase containing the base is recycled.
U.S. Pat. No. 6,395,933 describes a process for producing one or more 4-aminodiphenylamine intermediates comprising the steps of bringing an aniline or aniline derivative and nitrobenzene into reactive contact; and reacting the aniline and nitrobenzene in a confined zone at a suitable time and temperature, in the presence of a mixture comprising a strong base, a suitable phase transfer catalyst and an oxidant. Certain phase transfer catalysts may also function as the strong base, such as tetraalkylammonium hydroxides. Examples are given that show increased selectivity for reactions in the presence of air or hydrogen peroxide, with KOH as the strong base and tetramethylammonium chloride as the phase transfer catalyst. The example with hydrogen peroxide does not indicate an optimum amount of peroxide in going from a mole ratio of H2O2/NB=0 to 1.0, whereas conversion steadily dropped as mole ratio increased. No examples were given for an oxidant with a phase transfer catalysts that also functions as the strong base
The objective of the present invention is to provide a superior method for producing one or more 4-ADPA intermediates by reacting aniline and nitrobenzene in the presence of a strong organic base, or equivalent thereof, and an oxidant comprising hydrogen peroxide.